This invention relates to a two-component developer comprising a magnetic carrier and a magnetic toner.
In general, a two component developer is composed of a non-magnetic toner which does not contain magnetic particles and a magnetic carrier. In such a two component developer, toner particles are brought into tribocontact with carrier particles to be charged electrically. The toner particles stick to carrier particles electrostatically. The carrier particles are transferred on a sleeve to a developing region by magnetic force as they are rolling or dragging magnetically. Toner particles are also transferred continuously along with the carrier particles to the developing region.
The toner and the carrier used in the conventional two-component developer have been studied for the improvement of various properties. In particular, when the carrier is a binder-type and small in particle size, the toner can be contained at higher content than conventional. Therefore, the latitude of toner supply is enlarged and high quality and long life are achieved.
However, when the toner particles are not charged uniformly by tribocontact between the toner and the carrier, the charge amount of each toner particle is different. This is caused by the different size of toner particles and the electrification build-up properties of toner particles. Accordingly, small toner particles which are not charged sufficiently stick to the carrier particles weakly, and liable to leave from the carrier particles as they are rolled to be moved on a sleeve, with the result that the small toner particles come to fly in a copying machine. The flying toner particles cause the dirt inside the copying machine, the fogs in copied images and the like.
In general, the wind is blowing whirlingly in the specified direction inside the copying machine for removal of air. The flying toner particles are flowed with the wind toward various components. For example, the flying toner particles adhere to a wire line of an electric charger. If the wire line of the electric charger is made dirt by the adhered toner particles, the irregular charging of a photosensitive member, the defects of copied images and the like are brought about. When the dirt makes further progress, a number of toner particles accumulate on a toner-drop-prevention plate. The accumulated toner particles drop onto copying paper to make it dirt.
The flying toner particles cause the problems as above mentioned. But, these problems are not so serious when a copying process is repeated about 40000 times at low copying speed (about 15 cm/sec).
But, a high-speed copying process (about 45 cm/sec) has been required recently. In such a process, a developer is rolled and moved on a sleeve at much higher speed than before to generate much more flying toner particles. The problems caused by the flying toner particles have become more remarkable.
It is proposed to prevent from generating of flying toner particles, for example, that toner particles are charged smoothly or quickly to adhere strongly to carrier particles. But, the toner particles are moved at high speed and the flying toner particles generate inevitably. The suppress of the generation of flying toner is not sufficient.
On the other hand, a magnetic toner is known as one component toner. It may be proposed in order to prevent from generating of the flying toner particles that the magnetic properties of the magnetic toner is utilized to attract the toner particles onto a sleeve in a manner similar to carrier particles. But, such a conventional magnetic toner contains magnetic particles at the high content of about 30 wt %. Even if the magnetic toner is merely applied to a two-component developer as a toner component, the magnetic toner particles are hard to be transferred to electrostatic latent images and to form copied images with high density.